I had a similar problem last year. In my case it turned out to be a caliper seal had gone bad...instead of leaking it was sucking air into the system. The brakes would get bled and seem fine and very quickly the firm pedal was gone.

Once that was figured out it was corrected pretty easily.

I had a bad master last year and the symptoms where a half pedal.  That is the pedal would firm up half way down its travel.  Put a kit through but had the same problem so bought a new one, problem gone.  As soon as I fixed it one of the front calipers sprung a leak so had to put a kit through it.  Found that the PO had put stainless sleeves in all the calipers so that's one task I won't have to do.  Had the same problem when I first bought the car on having to pump the brakes.  Replaced my rear bearings and all came good.  Runout can give you real problems.

Thanks!  good thoughts - I will re-check the rear bearings and run out. I have also considered going to the SS sleeved brakes. I had replaced them with the standard NAPA rebuilds but who knows how good those are.

I believe the allowable runout is .003" TIR. I would shoot for .002" max.